Catalyst warming apparatus of internal combustion engine

ABSTRACT

It is an object of the present invention to provide a technology capable of producing an appropriate combustible mixture in an apparatus for heating an exhaust-purifying catalyst disposed in an exhaust passage of an internal combustion engine, without providing a special pre-mixing chamber for mixing fuel and air, by burning the combustible mixture in the exhaust passage upstream of the exhaust-purifying catalyst when the exhaust-purifying catalyst is inactive.  
     To achieve this object, in a catalyst warming apparatus of the internal combustion engine according to the present invention, a sub exhaust-purifying catalyst is disposed in the exhaust passage upstream of a main exhaust-purifying catalyst, and the fuel components and air are discharged from the internal combustion engine when the main exhaust-purifying catalyst needs to be warmed up. Thus, the fuel components and air discharged from the internal combustion engine are mixed into a combustible mixture in the sub exhaust-purifying catalyst, and the resultant combustible mixture is burned upstream of the main exhaust-purifying catalyst.

[0001] This is a continuation of application Ser. No. 09/690,392 filedOct. 17, 2000.

BACKGROUND ART

[0002] The present invention generally relates to a technology forpurifying the exhaust gas of internal combustion engines mounted inautomobiles and the like, and in particular, relates to a technology forimproving exhaust emissions by activating early on an exhaust-purifyingcatalyst disposed in an exhaust passage of the internal combustionengine.

[0003] In recent years, internal combustion engines mounted inautomobiles and the like are required to remove harmful gas componentscontained in the exhaust gas before discharging the exhaust gas into theair. With respect to such requirement, there has been proposed atechnology in which an exhaust-purifying catalyst that removes theharmful gas components contained in the exhaust gas is provided in anexhaust passage of an internal combustion engine.

[0004] As an exhaust-purifying catalyst described above, a wide varietyof exhaust-purifying catalysts have been developed including, forexample, a three-way catalyst, an NO_(x) occlusion reduction catalyst, aselective reduction NO_(x) catalyst, an oxidation catalyst, and anexhaust-purifying catalyst formed from an appropriate combination ofthese exhaust-purifying catalysts. These exhaust-purifying catalysts aregenerally capable of purifying the harmful gas components of the exhaustgas when activated at or higher than a predetermined temperature.Therefore, these exhaust-purifying catalysts cannot sufficiently purifythe harmful gas components of the exhaust gas at a temperature less thanthe predetermined temperature, for example, when the internal combustionengine is cold-started.

[0005] Particularly, when the internal combustion engine iscold-started, combustion of the mixture is likely to become unstable dueto low temperature within the cylinders. Therefore, the internalcombustion engine discharges a relatively large quantity of unburnedfuel components. If the exhaust-purifying catalyst is inactive, a largequantity of unburned fuel components is discharged into the air withoutbeing purified.

[0006] Accordingly, when the internal combustion engine is cold-started,it is important to activate the exhaust-purifying catalyst early on tosuppress degradation of the exhaust emissions during and immediatelyafter starting.

[0007] Regarding such a requirement, Japanese Patent No. 2710269discloses a proposal for a catalyst-heating burner for a spark-ignitionengine.

[0008] This catalyst-heating burner for the spark-ignition enginedescribed in the Patent Publication of the above-mentioned patentincludes an exhaust-purifying catalyst disposed in an exhaust passage ofthe internal combustion engine, and a combustor disposed in the exhaustpassage upstream of the exhaust-purifying catalyst. When the internalcombustion engine is warmed up after cold starting, half of thecylinders of the internal combustion engine are operated with a richmixture to produce a combustible gas, and fuel injection to the otherhalf is discontinued. The combustible gas discharged from the formerhalf cylinders and the air discharged from the latter half cylinders aremixed and burned in the combustor, thereby quickly heating theexhaust-purifying catalyst.

[0009] The combustor used in such a catalyst-heating burner for thespark-ignition engine has a chamber for mixing and burning thecombustible gas and the air. However, this chamber has a largercross-sectional area as compared to that of the exhaust passage and alarger heat capacity. Therefore, the heat of the exhaust gas would betransferred to the combustor when the combustor is not in operation.

[0010] Then, when the heat of the exhaust gas is transferred to thecombustor, the exhaust-purifying catalyst located downstream of thecombustor is cooled by the low-temperature exhaust gas, resulted in apossibility of lowering the temperature of the exhaust-purifyingcatalyst to a temperature less than the activation temperature.

[0011] Moreover, the combustor of the above-described catalyst-heatingburner for the spark ignition engine is located immediately downstreamof the exhaust branch pipes. Therefore, the combustible mixture withinthe combustor is liable to be affected by pulsation of the exhaust gas,whereby combustion of the combustible mixture is liable to becomeunstable. Moreover, an atmosphere temperature of the exhaust passage andthe combustor becomes low immediately after cold-starting of theinternal combustion engine, so that combustion of the combustiblemixture is apt to become unstable.

[0012] Such unstable combustion of the combustible mixture in thecombustor makes it difficult for the combustible mixture to becompletely burned up, and, it is possible to result in rather increasingquantity of unburned fuel components to be discharged into the air.

SUMMARY OF THE INVENTION

[0013] The present invention has been made in view of the foregoingconventional problems. A first object of the present invention is toprevent an undesirable temperature decrease of an exhaust-purifyingcatalyst during normal operation and suppress degradation of exhaustemissions, by providing a technology capable of mixing the combustiblegas and air, without providing a special combustion chamber dedicatedfor mixing the combustible gas and air, in an apparatus for warming anexhaust-purifying catalyst by burning the combustible mixture in anexhaust passage upstream of the exhaust-purifying catalyst.

[0014] A second object of the present invention is to preventdegradation of exhaust emissions caused by combustion of the combustiblemixture and activate an exhaust-purifying catalyst early on, byproviding a technology for stabilizing combustion of the combustiblemixture in an apparatus for warming an exhaust-purifying catalyst byburning the combustible mixture in an exhaust passage upstream of theexhaust-purifying catalyst.

[0015] First, the present invention employs the following means toachieve the foregoing first object.

[0016] More specifically, a catalyst warming apparatus of an internalcombustion engine according to the present invention includes: anexhaust passage connected to the internal combustion engine; a mainexhaust-purifying catalyst provided in the exhaust passage for purifyingexhaust gas flowing in the exhaust passage; a sub exhaust-purifyingcatalyst provided in the exhaust passage upstream of the mainexhaust-purifying catalyst for purifying the exhaust gas flowing in theexhaust passage; ignition means provided in the exhaust passage betweenthe main and sub exhaust-purifying catalysts; and combustible-componentsupply means for supplying fuel and air to the exhaust passage upstreamof the sub exhaust-purifying catalyst.

[0017] In a catalyst warming apparatus constructed as described above,the combustible-component supply means and the ignition means areactuated when the main exhaust-purifying catalyst needs to be heated.

[0018] When the combustible-component supply means is actuated, fuel andair are supplied to the exhaust passage upstream of the subexhaust-purifying catalyst and enter the sub exhaust-purifying catalyst.

[0019] The sub exhaust-purifying catalyst has a plurality of flowpassages each having a much smaller diameter as compared to that of theexhaust passage. Therefore, the fuel and air flowing in such small flowpassages are sufficiently mixed together. As a result, the gas flowingout from the sub exhaust-purifying catalyst is a combustible gasconsisting of a pre-mixed fuel and air, namely, a combustible mixture.

[0020] The combustible mixture discharged from the sub exhaust-purifyingcatalyst is ignited for combustion by the ignition means disposed in theexhaust passage between the sub and main exhaust-purifying catalysts.Hot burned gas produced by the combustion of the combustible mixtureenters the main exhaust-purifying catalyst located downstream of theignition means. When the burned gas flows through the mainexhaust-purifying catalyst, a large amount of heat is transferred fromthe burned gas to the main exhaust-purifying catalyst, whereby the mainexhaust-purifying catalyst is rapidly warmed up to an activationtemperature range.

[0021] Therefore, according to the catalyst warming apparatus of theinternal combustion engine according to the present invention, the fueland air are mixed in the sub exhaust-purifying catalyst. This obviatesthe need for providing a special pre-mixing chamber for mixing the fueland air. As a result, when the internal combustion engine is in thenormal operating state, the heat of the exhaust gas is not transferredto such pre-mixing chamber, so that the main exhaust-purifying catalystis not undesirably cooled by the low-temperature exhaust gas.

[0022] In the catalyst warming apparatus according to the presentinvention, the combustible-component supply means may supply the fueland air to the exhaust passage upstream of the sub exhaust-purifyingcatalyst immediately before completion of starting of the internalcombustion engine.

[0023] In this case, the main exhaust-purifying catalyst is warmed up tothe activation temperature range before the internal combustion enginestarts combustion of the mixture, in other words, before the internalcombustion engine discharges the burned mixture as exhaust gas.Therefore, harmful gas components in the exhaust gas could have beenpurified in the main exhaust-purifying catalyst at the time when theinternal combustion engine, after completion of starting operation,starts discharging the burned mixture as exhaust gas.

[0024] For supplying the fuel and air to the exhaust passage upstream ofthe sub exhaust-purifying catalyst immediately before completion ofstarting the internal combustion engine, the combustible-componentsupply means may be adapted to supply the fuel and air to the exhaustpassage upstream of the sub exhaust-purifying catalyst by allowingactuation of a fuel injection valve in every cylinder of the internalcombustion engine, and, at the same time, inhibiting actuation of aspark plug in every cylinder, during cranking of the internal combustionengine so that every cylinder discharges an unburned mixture.

[0025] For supplying the fuel and air to the exhaust passage upstream ofthe sub exhaust-purifying catalyst immediately before completion ofstarting the internal combustion engine, the combustible-componentsupply means may be adapted to supply the fuel and air to the exhaustpassage upstream of the sub exhaust-purifying catalyst by inhibitingactuation of the spark plug in every cylinder of the internal combustionengine, and, at the same time, allowing actuation of actuation of thefuel injection valve in one or more of the cylinders, during cranking ofthe internal combustion engine so that the aforementioned one or morecylinders discharge unburned mixture.

[0026] For supplying the fuel and air to the exhaust passage upstream ofthe sub exhaust-purifying catalyst immediately before completion ofstarting the internal combustion engine, the combustible-componentsupply means may be adapted to supply the fuel and air to the exhaustpassage upstream of the sub exhaust purifying catalyst, by allowingactuation of the fuel injection valve in every cylinder of the internalcombustion engine, and, at the same time, inhibiting actuation of thespark plug in one or more of the cylinders, during cranking of theinternal combustion engine so that the aforementioned one or morecylinders discharge unburned mixture.

[0027] Meanwhile, in the catalyst warming apparatus of the internalcombustion engine according to the present invention, thecombustible-component supply means may be adapted to supply the fuel andair to the exhaust passage upstream of the sub exhaust-purifyingcatalyst immediately after completion of starting of the internalcombustion engine.

[0028] In this case, the combustible mixture is burned in the exhaustpassage upstream of the main exhaust-purifying catalyst immediatelyafter starting of the internal combustion engine, and because of thisthe main exhaust-purifying catalyst is rapidly warmed up to theactivation temperature range.

[0029] As a result, degradation of exhaust emissions immediately afterstarting of the internal combustion engine can be suppressed even whenthe internal combustion engine is started with the main exhaustpurifying catalyst being in the inactive state.

[0030] For supplying the fuel and air to the exhaust passage upstream ofthe sub exhaust-purifying catalyst immediately before completion ofstarting the internal combustion engine, the combustible-componentsupply means may be adapted to supply the fuel and air to the exhaustpassage upstream of the sub exhaust-purifying catalyst by causing one ormore of the cylinders of the internal combustion engine to dischargeexhaust gas containing unburned fuel as well as causing the remainder ofthe cylinders to discharge exhaust gas containing unburned air,immediately after completion of starting of the internal combustionengine.

[0031] The combustible-component supply means may be adapted to causeone or more of the cylinders of the internal combustion engine todischarge the exhaust gas containing unburned fuel, by burning a richmixture in the aforementioned one or more cylinders so that the unburnedfuel remains in the exhaust gas discharged from the aforementioned oneor more cylinders.

[0032] The combustible-component supply means may be adapted to causethe aforementioned one or more cylinders of the internal combustionengine to discharge the exhaust gas containing unburned fuel, byinjecting main fuel for combustion from the fuel injection valve of theaforementioned one or more cylinders, and then, secondarily injectingfuel therefrom so that the unburned fuel is contained in the exhaust gasdischarged from the aforementioned one or more cylinders. The time forsecondarily injecting fuel may be the latter half of the expansionstroke of the aforementioned one or more cylinders or during the exhauststroke thereof, after finishing combustion of the main fuel.

[0033] The combustible-component supply means may be adapted to causeone or more of the cylinders of the internal combustion engine todischarge the exhaust gas containing unburned fuel, by causinglow-temperature combustion to occur in the aforementioned one or morecylinders. In this case, the fuel injected from the fuel injectionvalve(s) is not completely burned in the cylinder(s) of low-temperaturecombustion, whereby a relatively large quantity of unburned fuel remainsin the exhaust gas discharged from the cylinder(s).

[0034] Here, the method of performing the low-temperature combustion maybe exemplified by a method called an exhaust gas recirculation (EGR) forrecirculating some of the exhaust gas flowing in the exhaust system ofthe internal combustion engine into the intake system thereof.

[0035] The combustible-component supply means may be adapted to causethe other cylinder(s) of the internal combustion engine to discharge theexhaust gas containing unburned air, by burning a lean mixture in theaforementioned other cylinder(s).

[0036] The combustible component supply means may be adapted to causethe other cylinder(s) of the internal combustion engine to discharge theexhaust gas containing unburned air, by inhibiting actuation of the fuelinjection valve(s) of the aforementioned other cylinder(s).

[0037] The combustible-component supply means may be adapted to supplythe fuel and air to the exhaust passage upstream of the subexhaust-purifying catalyst by burning a rich mixture in every cylinderof the internal combustion engine, and, at the same time, supplying subair to the exhaust passage upstream of the sub exhaust-purifyingcatalyst, immediately after completion of starting of the internalcombustion engine. Note that the expression “the exhaust passageupstream of the sub exhaust-purifying catalyst” as used herein refers tothe passage from the combustion chambers of the internal combustionengine to the sub exhaust-purifying catalyst, and for example, includesan exhaust passage connected to exhaust ports formed in the internalcombustion engine or the exhaust passage connected to the internalcombustion engine.

[0038] The catalyst warming apparatus of the internal combustion engineaccording to the present invention may further include flame back-flowpreventing means for preventing flame of the combustible mixture ignitedby the ignition means from flowing backward in the exhaust passage.

[0039] In this case, since the flame of the combustible mixture ignitedby the ignition means does not flow backward in the exhaust passage, theflame is stabilized, and the main exhaust-purifying catalyst can bereliably heated.

[0040] Here, the flame back-flow preventing means may be a wire meshhaving a multiplicity of holes of a diameter equal to or smaller than aflame-quenching diameter. However, it is preferable to make the diameterof the exhaust passage in the sub exhaust-purifying catalyst equal to orsmaller than the flame-quenching diameter so as to add the function ofthe flame back-flow preventing means to the sub exhaust-purifyingcatalyst.

[0041] In the catalyst warming apparatus of the internal combustionengine according to the present invention, the main exhaust-purifyingcatalyst may be a so-called wall-flow catalyst that includes a porousbase material including a flow passage having its upstream end open anddownstream end closed, and a flow passage having its upstream end closedand downstream end open, wherein the former flow passage and the latterflow passage are alternately arranged in a honeycomb pattern.

[0042] Thus, any soot or the like produced by the combustion of thecombustible mixture is removed by the main exhaust-purifying catalyst,whereby degradation of exhaust emissions due to the combustion of thecombustible mixture-is prevented.

[0043] In the catalyst warming apparatus of the internal combustionengine according to the present invention, the ignition means may bedisposed so that the flame resulting from ignition of the combustiblemixture is produced in a portion upstream of a catalyst carrier withinthe main exhaust-purifying catalyst. Preferably, the portion upstream ofthe catalyst carrier within the main exhaust-purifying catalyst has aheat insulated structure.

[0044] According to such a catalyst warming apparatus of the internalcombustion engine having the above-described structure, the combustiblemixture is burned in the portion upstream of the catalyst carrier withinthe main exhaust-purifying catalyst. This obviates the need for aspecial combustion chamber for burning the combustible chamber. As aresult, the heat of the exhaust gas is not transferred to the combustionchamber when the internal combustion engine is in the normal operatingstate.

[0045] The catalyst warming apparatus of the internal combustion engineaccording to the present invention may further include air supply meansfor supplying only the air to the exhaust passage upstream of the subexhaust-purifying catalyst for a predetermined period after completionof heating the main exhaust-purifying catalyst.

[0046] In this case, only the air is supplied to the exhaust passageupstream of the sub exhaust-purifying catalyst for the predeterminedperiod after completion of heating the main exhaust-purifying catalyst.Therefore, the combustible mixture remaining in the exhaust passage fromthe sub exhaust-purifying catalyst to the ignition means is completelyremoved. As a result, combustion of the combustible mixture does notoccur in the exhaust passage after completion of heating the mainexhaust-purifying catalyst.

[0047] Note that, when the catalyst warming apparatus of the internalcombustion engine according to the present invention is structured so asto heat the main exhaust-purifying catalyst before starting the internalcombustion engine, the catalyst warming apparatus preferably furtherincludes: air supply means for supplying only air to the exhaust passageupstream of the sub exhaust-purifying catalyst for a predeterminedperiod after the main exhaust-purifying catalyst is warmed up to adesired temperature range; and engine starting means for starting theinternal combustion engine after a lapse of the predetermined period.

[0048] The present invention employs the following means to achieve theforegoing second object.

[0049] More specifically, the catalyst warming apparatus of the internalcombustion engine according to the present invention further includes:exhaust throttling means for throttling a flow rate of the exhaust gasflowing in the exhaust passage when the combustible-component supplymeans is supplying the fuel and air to the exhaust passage upstream ofthe sub exhaust-purifying catalyst, in addition to the exhaust passageconnected to the internal combustion engine; a main exhaust-purifyingcatalyst provided in the exhaust passage for purifying the exhaust gasflowing in the exhaust passage; a sub exhaust-purifying catalystprovided in the exhaust passage upstream of the main exhaust-purifyingcatalyst for purifying the exhaust gas flowing in the exhaust passage;ignition means provided in the exhaust passage between the main and subexhaust-purifying catalysts; and combustible-component supply means forsupplying fuel and air to the exhaust passage upstream of the subexhaust-purifying catalyst.

[0050] In such a catalyst warming apparatus of an internal combustionengine structured as described above, when the main exhaust-purifyingcatalyst needs to be heated, the combustible-component supply means andthe ignition means are actuated and the exhaust throttling meansthrottles the flow rate in the exhaust passage.

[0051] In this case, since the exhaust throttling means throttles theflow rate in the exhaust passage, pressure in the exhaust passage fromthe internal combustion engine to the exhaust throttling means isincreased, whereby pulsation of the exhaust gas discharged from theinternal combustion engine is suppressed.

[0052] As a result, ignitability of the combustible mixture is improvedand combustion of the combustible mixture is stabilized, therebyenabling the exhaust-purifying catalyst to be reliably heated.

[0053] Note that, in the catalyst warming apparatus of the internalcombustion engine according to the present invention, the exhaustthrottling means may be provided in the exhaust passage down-stream ofthe ignition means, and preferably, provided in the exhaust passagedownstream of the main exhaust-purifying catalyst.

[0054] In this case, when the exhaust throttling means throttles theflow rate of the exhaust gas in the exhaust passage, the pressure in theexhaust passage is increased, whereby pulsation of the exhaust gas issuppressed. Moreover, an atmospheric temperature in the vicinity of theignition means is raised, whereby ignitability of the combustiblemixture is improved.

[0055] When the exhaust throttling means is disposed in the exhaustpassage downstream of the main exhaust-purifying catalyst, burned gas ofthe combustible mixture flows through the main exhaust-purifyingcatalyst at a low velocity due to the throttled flow rate of the exhaustgas in the exhaust passage by the exhaust throttling means. Therefore,the heat of the burned gas is efficiently transferred to the mainexhaust-purifying catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

[0056]FIG. 1 is a diagram showing a schematic structure of an internalcombustion engine to which a catalyst warming apparatus according to thepresent invention is applied;

[0057]FIG. 2 is a first diagram illustrating an internal structure of asecond exhaust-purifying catalyst;

[0058]FIG. 3 is a second diagram illustrating the internal structure ofthe second exhaust-purifying catalyst;

[0059]FIG. 4 is a block diagram showing an internal structure of anelectronic control unit (ECU);

[0060]FIG. 5 is a flowchart illustrating a catalyst-heating controlroutine according to Embodiment 1;

[0061]FIG. 6 is a flowchart illustrating a catalyst-heating controlroutine according to Embodiment 2;

[0062]FIG. 7 is a flowchart illustrating a catalyst-heating controlroutine according to Embodiment 3;

[0063]FIG. 8 is a flowchart illustrating a catalyst-heating controlroutine according to Embodiment 4;

[0064]FIG. 9 is a diagram showing a schematic structure of an internalcombustion engine to which a catalyst warming apparatus according toEmbodiment 5 is applied;

[0065]FIG. 10 is a block diagram showing an internal structure of an ECUaccording to Embodiment 5;

[0066]FIG. 11 is a flowchart illustrating a catalyst-heating controlroutine according to Embodiment 5;

[0067]FIG. 12 is a flowchart illustrating a catalyst-heating controlroutine according to Embodiment 6;

[0068]FIG. 13 is a diagram showing a schematic structure of an internalcombustion engine to which a catalyst warming apparatus according toEmbodiment 7 is applied;

[0069]FIG. 14 is a block diagram showing an internal structure of an ECUaccording to Embodiment 7; and

[0070]FIG. 15 is a flowchart illustrating a catalyst-heating controlroutine according to Embodiment 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0071] Hereinafter, specific embodiments of a catalyst warming apparatusof an internal combustion engine according to the present invention willbe described referring to the accompanying drawings.

[0072] Embodiment 1

[0073] First, a catalyst warming apparatus of an internal combustionengine according to Embodiment 1 of the present invention will bedescribed with reference to FIGS. 1 to 5.

[0074]FIG. 1 is a diagram showing a schematic structure of the internalcombustion engine to which the catalyst warming apparatus of the presentembodiment is applied, and intake and exhaust systems thereof.

[0075] The internal combustion engine 1 of FIG. 1 is a four-cycle,water-cooled gasoline engine having four cylinders 2 a. The internalcombustion engine 1 is provided with spark plugs 2 b that facerespective combustion chambers of the cylinders 2 a. The internalcombustion engine 1 is also provided with fuel injection valves 3 havingtheir injection ports facing the respective combustion chambers of thecylinders 2 a.

[0076] Each fuel injection valve 3 communicates with a fuel distributionpipe 4, which in turn communicates with an unillustrated fuel pump. Thefuel distribution pipe 4 receives the fuel discharged from the fuelpump, and distributes the received fuel to each fuel injection valve 3.

[0077] The fuel injection valves 3 are connected to respective drivingcircuits 5 through electrical wiring, so that each fuel injection valve3 is opened to inject the fuel in response to an electric driving powerapplied thereto from the associated driving circuit 5.

[0078] Inlet branch pipes 6 are connected to the internal combustionengine 1 so as to communicate with the respective combustion chambers ofthe cylinders 2 a through unillustrated respective inlet ports.

[0079] The inlet branch pipes 6 are connected to a surge tank 7, whichin turn is connected to an air cleaner box 9 through an inlet pipe 8.

[0080] The inlet pipe 8 is provided with a throttle valve 10 cooperatingwith an unillustrated accelerator pedal for adjusting the flow rate ofthe intake air flowing in the inlet pipe 8. The throttle valve 10 isprovided with a throttle-position sensor 11 for outputting an electricsignal corresponding to a degree of opening of the throttle valve 10.

[0081] An airflow meter 12 for outputting an electric signalcorresponding to the mass of the intake air flowing in the inlet pipe 8is provided in the inlet pipe 8 upstream of the throttle valve 10.

[0082] Exhaust branch pipes 13 are connected to the internal combustionengine 1 so as to communicate with the respective combustion chambers ofthe cylinders 2 a through unillustrated respective exhaust, ports. Theexhaust branch pipes 13 are connected to an exhaust pipe 14, which inturn is connected to an unillustrated muffler in the downstream of theexhaust pipe 14.

[0083] The exhaust pipe 14 is provided with a first exhaust-purifyingcatalyst 15 for purifying harmful gas components contained in theexhaust gas flowing in the exhaust pipe 14. The first exhaust-purifyingcatalyst 15 is one embodiment of a sub exhaust-purifying catalystaccording to the present invention. For example, the firstexhaust-purifying catalyst 15 is a three-way catalyst that includes alattice-like ceramic carrier of cordierite having a plurality of throughholes extending along a exhaust gas flowing direction, and a catalyticlayer that is coated over the surface of the ceramic carrier. Thecatalytic layer is formed from a platinum-rhodium (Pt—Rh)-based orpalladium-rhodium (Pd—Rh)-based precious metal catalytic substancecarried on the surface of porous alumina (Al) having a multiplicity ofpores.

[0084] The first exhaust-purifying catalyst 15 as structured above isactivated at a temperature equal to or above a predeterminedtemperature. When the exhaust gas, having an air-fuel ratio close to adesirable ratio, is introduced into the first exhaust-purifying catalyst15, the first exhaust-purifying catalyst 15 reacts hydrocarbon (HC) andcarbon monoxide (CO) contained in the exhaust gas with oxygen (O₂)therein, thereby oxidizing HC and CO into water (H₂O) and carbon dioxide(CO₂). At the same time, the first exhaust-purifying catalyst 15 reactsnitrogen oxide (NO_(x)) in the exhaust gas with HC and CO therein,thereby reducing NO_(x) to water (H₂O), carbon dioxide (CO₂) andnitrogen (N₂).

[0085] The exhaust pipe 14 is provided with a second exhaust-purifyingcatalyst 16 downstream of the first exhaust-purifying catalyst 15. Thesecond exhaust-purifying catalyst 16 is one embodiment of a mainexhaust-purifying catalyst according to the present invention, andincludes a casing 16 a formed by a cylindrical body having tapered coneportions at both ends, and a catalyst body 16 b disposed within thecylindrical body of the casing 16 a.

[0086] As shown in FIGS. 2 and 3, the catalyst body 16 b is a wall-flowexhaust-purifying catalyst that is formed by a porous carrier and acatalytic layer formed on the surface of the porous carrier. The porouscarrier includes first and second flow passages 160, 161, respectively,that are arranged in a honeycomb pattern. The first flow passage 160 hasits upstream end opened and downstream end closed, whereas the secondflow passage 161 has its upstream end closed and downstream end opened.

[0087] The above-described carrier may include, for example, porousceramics and zeolite, and the catalytic layer may include a catalyticlayer formed from a platinum-rhodium (Pt—Rh)-based or palladium-rhodium(Pd—Rh)-based precious metal catalytic substance carried on the surfaceof porous alumina (Al), or a catalytic layer formed from (i) at leastone element selected from a group consisting of an alkali metal, such aspotassium (K), sodium (Na), lithium (Li) or cesium (Cs), an alkalineearth metal, such as barium (Ba) or calcium (Ca), and a rare earthelement, such as lanthanum (La) or yttrium (Y), and (ii) a preciousmetal such as platinum (Pt).

[0088] In the second exhaust-purifying catalyst 16 structured asdescribed above, the exhaust gas entering the second exhaust-purifyingcatalyst 16 is first introduced into the first flow passages 160, andthen, through pores formed in the wall of the carrier into the secondflow passages 161. Thereafter, the exhaust gas is discharged from thesecond flow passages 161 into the downstream exhaust pipe 14.

[0089] While the exhaust gas is flowing through the pores in the wall ofthe carrier, the carrier collects particulate matter such as soot andunburned fuel components contained in the exhaust gas, and the catalyticlayer on the surface of the carrier purifies harmful gas componentscontained in the exhaust gas.

[0090] Referring back to FIG. 1, the cone portion located upstream ofthe catalyst body 16 b in the casing 16 a of the secondexhaust-purifying catalyst 16 is provided with an ignition device 17formed by a piezoelectric element. This ignition device 17 implementsignition means according to the present invention.

[0091] This cone portion of the casing 16 a is preferably formed of aheat insulated structure. A method of forming the cone portion with theheat insulated structure may include, for example, applying a ceramiccoating over the inner wall surface of the cone portion, forming theouter wall of the cone portion to have a double structure and providinga vacuum layer between the wall surfaces of the double structure, andother methods may be used to provide the heat insulated structure of thecone portion.

[0092] The exhaust pipe 14 is provided with an air-fuel ratio sensor 18between the first exhaust-purifying catalyst 15 and the secondexhaust-purifying catalyst 16. The air-fuel ratio sensor 18 outputs anelectric signal corresponding to the air-fuel ratio of the exhaust gasflowing in the exhaust pipe 14, i.e., the air-fuel ratio of the exhaustgas entering the second exhaust-purifying catalyst 16.

[0093] The air-fuel ratio sensor 18 is formed by, for example, a solidelectrolyte portion formed from zirconia (ZrO₂) baked into a cylindricalshape, an outer platinum electrode covering the outer surface of thesolid electrolyte portion, and an inner platinum electrode covering theinner surface of the solid electrolyte portion. When a voltage isapplied between the electrodes, the air-fuel ratio sensor 18 outputs avoltage value proportional to the oxygen concentration in the exhaustgas (concentration of unburned gas components when the air-fuel ratio isricher than the theoretical air-fuel ratio) resulting from migration ofoxygen ions.

[0094] The exhaust pipe 14 is provided with an exhaust throttle valve 19downstream of the second exhaust-purifying catalyst 16. The exhaustthrottle valve 19 adjusts the flow rate of the exhaust gas flowing inthe exhaust pipe 14. The exhaust throttle valve 19 is provided with anexhaust-throttling actuator 20 formed by a stepper motor and the likefor opening and closing the exhaust throttle valve 19 according to themagnitude of applied electric power.

[0095] The internal combustion engine 1 is provided with acrank-position sensor 21 for outputting a pulse signal every time acrankshaft (not shown) is rotated a predetermined angle (e.g., 10degrees). The crank-position sensor 21 is formed by a timing rotormounted to the end of the crankshaft, and an electromagnetic pickupattached to a cylinder block of the internal combustion engine 1.

[0096] The internal combustion engine 1 is also provided with awater-temperature sensor 22 for outputting an electric signalcorresponding to the temperature of cooling water flowing in a waterjacket formed in the cylinder block and cylinder head of the internalcombustion engine 1.

[0097] The internal combustion engine 1 structured as described abovefurther includes an electronic control unit (ECU) 23 for controlling theinternal combustion engine 1. Various sensors such as thethrottle-position sensor 11, the airflow meter 12, the air-fuel ratiosensor 18, the crank-position sensor 21, and the water-temperaturesensor 22 are connected to the ECU 23 through electrical wiring, so thatthe output signals of the sensors are input to the ECU 23.

[0098] Further, the spark plugs 2 b, driving circuits 5, ignition device17, and exhaust-throttling actuator 20 are connected to the ECU 23through electrical wiring, so that the ECU 23 can control them by usingthe output signal values of the sensors as parameters.

[0099] As shown in FIG. 4, the ECU 23 includes a central processing unit(CPU) 25, a read only memory (ROM) 26, a random access memory (RAM) 27,a backup RAM 28, an input port 29, and an output port 31, which areconnected to each other through a bidirectional bus 24. The ECU 23further includes an analog/digital (A/D) converter (A/D) 30 connected tothe input port 29.

[0100] The input port 29 receives an output signal from a sensor thatoutputs a signal in digital form, such as the crank-position sensor 21,and transmits the signal to the CPU 25 and/or the RAM 27.

[0101] Further, the input port 29 receives, through the A/D converter30, output signals from sensors that outputs signals in analog form,such as the throttle-position-sensor 11, the airflow meter 12, theair-fuel ratio sensor 18 and the water-temperature sensor 22, andtransmits the signals to the CPU 25 and/or the RAM 27.

[0102] The output port 31 is connected to the spark plugs 2 b, thedriving circuits 5, the ignition device 17 and the exhaust-throttlingactuator 20 through electrical wiring so as to transmit a control signaloutputted from the CPU 25 to the spark plugs 2 b, the driving circuits5, the ignition device 17 or the exhaust-throttling actuator 20.

[0103] The ROM 26 stores various application programs such as anignition-timing control routine for determining the ignition timing ofeach spark plug 2 b, a fuel injection volume control routine fordetermining the fuel quantity to be injected from each fuel injectionvalve 3, an air-fuel ratio feedback control routine for performingair-fuel ratio feedback-controlling of the fuel injection volume, a fuelinjection timing control routine for determining the fuel injectiontiming of each fuel injection valve 3, and an exhaust-throttling controlroutine for deter-mining the opening degree of the exhaust throttlevalve 19, and in addition, the ROM 26 stores a catalyst-heating controlroutine for heating the second exhaust-purifying catalyst 16.

[0104] In addition to these application programs, the ROM 26 furtherstores various control maps. The control maps include, for example, anignition-timing control map indicating the relation between theoperating state of the internal combustion engine 1 and the ignitiontiming, a fuel injection volume control map indicating the relationbetween the operating state of the internal combustion engine 1 and thefuel injection volume, a fuel injection timing control map indicatingthe relation between the operating state of the internal combustionengine 1 and the fuel injection timing, and anexhaust-throttle-valve-opening control map indicating the relationbetween the operating state of the internal combustion engine 1 and theopening degree of the exhaust throttle valve 19.

[0105] The RAM 27 stores the output signals from the sensors,calculation results of the CPU 25, and the like. The calculation resultsinclude, for example, an engine speed calculated from the output signalof the crank-position sensor 21. The data is updated every time thecrank-position sensor 21 outputs a signal.

[0106] The backup RAM 28 is a non-volatile memory capable of storingdata even after the internal combustion engine 1 is stopped, and itstores a learning value relating to the ignition control, a learningvalue relating to the fuel-injection control, a learning value relatingto the exhaust-throttling control and the like.

[0107] The CPU 25 operates according to the application programs storedin the ROM 26. The CPU 25 determines the operating state of the internalcombustion engine 1 from the output signals of the sensors stored in theRAM 27. Based on the determined operating state and the control maps,the CPU 25 executes controls such as ignition control and fuel-injectioncontrol, and also executes the catalyst-heating control that is thesubject matter of the present invention.

[0108] The catalyst-heating control is the control for activating thecatalyst body 16 b of the second exhaust-purifying catalyst 16 early on,and this control is executed when the internal combustion engine 1 isstarted with the first and second exhaust-purifying catalysts 15, 16being inactive, such as when the internal combustion engine 1 iscold-started.

[0109] In the catalyst-heating control, the CPU 25 first determineswhether at least one of the first and second exhaust-purifying catalysts15, 16 is active or not when the internal combustion engine 1 isstarted.

[0110] When the CPU 25 determines that both the first and secondexhaust-purifying catalysts 15, 16 are inactive, the CPU 25 executes acatalyst-heating process in order to activate the secondexhaust-purifying catalyst 16 early on. When the CPU 25 determines thatat least one of the first and second exhaust-purifying catalysts 15, 16is active, and preferably, if the CPU 25 determines that the secondexhaust-purifying catalysts 16 is active, the CPU 25 does not executethe catalyst-heating process.

[0111] In the catalyst-heating process, the CPU 25 first inhibitsapplication of the driving electric power to the spark plugs 2 b, andactuates the unillustrated starter motor, and at the same time, the CPU25 applies the driving electric power to the driving circuits 5 toactuate the fuel injection valves 3. Then, the CPU 25 applies thedriving electric power to the ignition device 17.

[0112] In this case, each cylinder 2 a of the internal combustion engine1 is supplied with air and fuel. However, since the spark plugs 2 b arenot actuated, each cylinder 2 a discharges the air and fuel still in theunburned state.

[0113] The air and fuel discharged from each cylinder 2 a flow into thefirst exhaust-purifying catalyst 15 through the exhaust branch pipes 13and the exhaust pipe 14. Since the exhaust passage in the firstexhaust-purifying catalyst 15 has an extremely smaller diameter ascompared to that of the exhaust pipe 14, the air and fuel are mixedtogether while they are flowing through the exhaust passage of suchsmaller diameter. As a result, when the air and fuel leave the firstexhaust-purifying catalyst 15, they becomes a well-mixed, excellentcombustible mixture.

[0114] The combustible mixture flowing out of the firstexhaust-purifying catalyst 15 reaches the second exhaust-purifyingcatalyst 16 through the exhaust pipe 14. The combustible mixture reachesand enters the second exhaust-purifying catalyst 16 is ignited andburned by the ignition device 17 provided at the cone portion upstreamof the catalyst body 16 b in the casing 16 a of the secondexhaust-purifying catalyst 16. Since the ignition device 17 is locatedimmediately upstream of the catalyst body 16 b, the flame of thecombustible mixture rapidly heats the catalyst body 16 b.

[0115] Moreover, the second exhaust-purifying catalyst 16 of the presentembodiment is a wall-flow exhaust-purifying catalyst. Therefore, anysoot or the like produced by such combustion of the combustible mixturewould be captured by the second exhaust-purifying catalyst 16, andtherefore, would not be discharged into the air.

[0116] Note that, in the present embodiment, in preparation foroccurrence of back-flow of the flame generated by the combustion of thecombustible mixture toward upstream of the ignition device 17, theexhaust flow passage in the first exhaust-purifying catalyst 15 isformed to have a diameter smaller than a flame-quenching diameter. As aresult, the flame generated by the combustion of the combustible mixturedoes not back-flow toward upstream of the first exhaust-purifyingcatalyst 15, whereby combustion of the combustible mixture isstabilized.

[0117] Additionally, in the catalyst-heating process of the presentembodiment, the CPU 25 also closes the exhaust throttle valve 19 to apredetermined degree. As a result, a pressure within the exhaust passagefrom the internal combustion engine 1 to the exhaust throttle valve 19is increased. Then, pulsation of the exhaust gas is suppressed by theincreased pressure and the temperature within the exhaust passage isincreased. Thus, the ignitability and combustion stability of thecombustible mixture are improved.

[0118] The above-described catalyst-heating process is continued for apredetermined time. The predetermined time is a time period required forraising the temperature of the catalyst body 16 b to the activationtemperature by the catalyst-heating process, and the time period isexperimentally obtained in advance.

[0119] Note that the predetermined time may be either a fixed time valueor a variable time value that is varied according to a catalyst-bedtemperature of the catalyst body 16 b upon starting of the internalcombustion engine 1.

[0120] After continuing execution of the catalyst-heating process forthe predetermined time, the CPU 25 executes a combustible-mixtureremoving process for a predetermined time to completely remove thecombustible mixture remaining in the exhaust passage from the internalcombustion engine 1 to the ignition device 17.

[0121] In the combustible-mixture removing process, the CPU 25 performs,for example, inhibition of application of the driving electric power tothe spark plugs 2 b, and further, inhibition of application of thedriving electric power to the driving circuits 5, and controlling of theexhaust-throttling actuator 20 so as to fully open the exhaust throttlevalve 19.

[0122] In this case, each cylinder 2 a of the internal combustion engine1 is supplied only with air and therefore, each cylinder 2 a dischargesthat air. The air discharged from each cylinder 2 a sequentially flowsthrough the exhaust branch pipes 13, the exhaust pipe 14, the firstexhaust-purifying catalyst 15, the exhaust pipe 14, the secondexhaust-purifying catalyst 16, and the exhaust pipe 14.

[0123] At this time, since the exhaust throttle valve 19 is fullyopened, the air discharged from each cylinder 2 a rushes into and flowsthrough the exhaust branch pipes 13, the exhaust pipe 14, the firstexhaust-purifying catalyst 15, the exhaust pipe 14, the secondexhaust-purifying catalyst 16, and the exhaust pipe 14.

[0124] As a result, the combustible mixture that remains in the exhaustpassage extending from the internal combustion engine 1 to the secondexhaust-purifying catalyst 16 (i.e., in the exhaust branch pipes 13, theexhaust pipe 14, the first exhaust-purifying catalyst 15, and theexhaust pipe 14) is forced into the second exhaust-purifying catalyst 16by the air flowing through the exhaust passage. Thus, the combustiblemixture is purified in the catalyst body 16 b activated by thecatalyst-heating process.

[0125] After executing the combustible-mixture removing process for thepredetermined time, the CPU 25 starts application of the drivingelectric power to the spark plugs 2 b and the driving circuits 5, andstarts the internal combustion engine 1. Since the combustible mixtureremaining in the exhaust passage extending from the internal combustionengine 1 to the second exhaust-purifying catalyst 16 has been completelyremoved, no flame is generated in a broad range covering from thecylinders 2 a of the internal combustion engine 1 to the secondexhaust-purifying catalyst 16.

[0126] Hereinafter, the catalyst-heating control of the presentembodiment will be described in detail.

[0127] The CPU 25 executes a catalyst-heating control routine as shownin FIG. 5 in order to execute the catalyst-heating control.

[0128] The catalyst-heating control routine is a routine that ispre-stored in the ROM 26 for execution upon starting of the internalcombustion engine 1.

[0129] In the catalyst-heating control routine, the CPU 25 firstdetermines in Step S501 whether the first or second exhaust-purifyingcatalyst 15, 16 is active or not.

[0130] The method for determining whether the first or secondexhaust-purifying catalyst is active may include, for example, thedetermination of whether the respective catalyst-bed temperatures of thefirst and second exhaust-purifying catalysts 15, 16 have been lowered toa temperature lower than the respective activation temperatures or not,based on the time elapsed from the last stopping of operation of theinternal combustion engine to restarting thereof 1; attaching atemperature sensor for detecting a catalyst-bed temperature to each ofthe first and second exhaust-purifying catalysts 15, 16, and determiningwhether the output signal values of the respective temperature sensorsare less than the respective activation temperatures or not; or byestimating the respective catalyst-bed temperatures of the first andsecond exhaust-purifying catalysts 15, 16 from the output signal(cooling-water temperature) of the temperature sensor 22, anddetermining whether the estimated values are less than the respectiveactivation temperatures or not.

[0131] When the CPU 25 determines in Step S501 that at least one of thefirst and second exhaust-purifying catalysts 15, 16 is active(preferably, the second exhaust-purifying catalyst 16 is determinedactive), the CPU 25 terminates execution of this routine and executesthe normal start control.

[0132] When the CPU 25 determines in Step S501 that both the first andsecond exhaust-purifying catalysts 15, 16 are inactive, the CPU 25proceeds to Step S502 and starts execution of the catalyst-heatingprocess. More specifically, the CPU 25 controls the exhaust-throttlingactuator 20 so as to close the exhaust throttle valve 19 to thepredetermined degree. Thereafter, the CPU 25 starts application of thedriving electric power to the starter motor, driving circuits 5corresponding to the fuel injection valves 3 of all the cylinders 2 a,and the ignition device 17, and, at the same time, inhibitingapplication of the driving electric power to the spark plugs 2 b of allthe cylinders 2 a.

[0133] In Step S503, the CPU 25 updates a counter value of a firstcounter C1 for counting the execution time of the catalyst-heatingprocess.

[0134] In Step S504, the CPU 25 determines whether the counter value ofthe first counter C1 updated in Step S503 is at least equal to or higherthan a predetermined value CS1 or not, i.e., whether or not thecatalyst-heating process has been executed at least for thepredetermined time or longer.

[0135] When the CPU 25 determines in Step S504 that the counter value ofthe first counter C1 is less than the predetermined value CS1, the CPU25 again executes Step S503 and subsequent steps.

[0136] On the other hand, when the CPU 25 determines in Step S504 thatthe counter value of the first counter C1 is equal to or higher than thepredetermined value CS1, the CPU 25 proceeds to Step S505 and startsexecution of the combustible-mixture removing process. Morespecifically, the CPU 25 inhibits application of the driving electricpower to the driving circuits 5 corresponding to all the cylinders 2 a,spark plugs 2 b of all the cylinders 2 a, and the ignition device 17,while continuing actuation of the starter motor, and, at the same time,the CPU 25 also controls the exhaust-throttling actuator 20 so that theexhaust throttle valve 19 is returned to the full-open state.

[0137] In Step S506, the CPU 25 updates a counter value of a secondcounter C2 for counting the execution time of the combustible-mixtureremoving process.

[0138] In Step S507, the CPU 25 determines whether the counter value ofthe second counter C2 updated in Step S506 is at least equal to apredetermined value CS2 or not, i.e., whether or not thecombustible-mixture removing process has been executed at least for thepredetermined time or longer.

[0139] When the CPU 25 determines in Step S507 that the counter value ofthe second counter C2 is less than the predetermined value CS2, the CPU25 repeats execution of Step S506 and subsequent steps.

[0140] On the other hand, when the CPU 25 determines in Step S507 thatthe counter value of the second counter C2 is equal to the predeterminedvalue CS2 or more, the CPU 25 proceeds to Step S508 and terminatesexecution of the combustible-mixture removing process.

[0141] In Step S509, the CPU 25 resets the respective counter values ofthe first and second counters C1, C2 to “zero” and terminates executionof this routine. Thereafter, the CPU 25 executes the normal engine-startcontrol.

[0142] According to the above-described catalyst-heating controlroutine, when the internal combustion engine 1 is started with the firstand second exhaust-purifying catalysts 15, 16 being inactive, such aswhen the internal combustion engine 1 is cold-started, fuel and air aresupplied to the exhaust pipe 14 upstream of the first exhaust-purifyingcatalyst 15, thereby the fuel and air are sufficiently mixed togetherwithin the first exhaust-purifying catalyst 15, resulting in forming anexcellent combustible mixture.

[0143] This combustible mixture is burned by the ignition device 17provided in the cone portion of the second exhaust-purifying catalyst16, and the catalyst body 16 b is heated by the flame produced by thecombustion of the combustible mixture.

[0144] At this time, since the exhaust throttle valve 19 has throttledthe flow rate in the exhaust pipe 14, pulsation of the exhaust gasdischarged from the internal combustion engine 1 is suppressed, and theatmosphere temperature within the exhaust passage is raised. As aresult, the ignitability and combustion stability of the combustiblemixture are improved. Moreover, when the flow rate in the exhaustpassage is throttled by the exhaust throttle valve 19, the velocity atwhich the burned gas of the combustible mixture flows through thecatalyst body 16 b is decreased. Therefore, heat-conduction efficiencyfrom the burned gas to the catalyst body 16 b is improved.

[0145] Thus, according to the catalyst warming apparatus of the internalcombustion engine of the present embodiment, the first exhaust-purifyingcatalyst 15 is disposed upstream of the second exhaust-purifyingcatalyst 16 to be heated, and the ignition device 17 is disposed at thecone portion of the second exhaust-purifying catalyst 16. Therefore, thefuel and air can be sufficiently mixed and desirably burned withoutproviding a special pre-mixing chamber for mixing the fuel and air and aspecial combustion chamber for burning the fuel and air.

[0146] As a result, when the internal combustion engine is in the normaloperating state, the heat of the exhaust gas is not transferred to thepre-mixing chamber, combustion chamber and the like, whereby the exhaustgas at a low temperature does not flow into the exhaust-purifyingcatalyst. Thus, the temperature of the exhaust-purifying catalyst can beprevented from being lowered to a value less than the activationtemperature, whereby degradation of the exhaust emissions is avoided.

[0147] According to the catalyst warming apparatus of the internalcombustion engine of the present embodiment, the secondexhaust-purifying catalyst 16 is a wall-flow catalyst. Therefore, evenif particulate matter (PM) such as soot is produced by combustion of thecombustible mixture, the PM is caught by the second exhaust-purifyingcatalyst 16, and is not discharged into the air.

[0148] According to the catalyst warming apparatus of the internalcombustion engine of the present embodiment, the cone portion of thesecond exhaust-purifying catalyst 16 has a heat insulated structure.Therefore, the heat generated by combustion of the combustible mixtureis not radiated through the wall surface of the cone portion. Thus,substantially all of the heat generated by combustion of the combustiblemixture can be transferred to the catalyst body 16 b.

[0149] According to the catalyst warming apparatus of the internalcombustion engine of the present embodiment, only the air is dischargedfrom the internal combustion engine 1 for a pre-determined period aftercompletion of heating the second exhaust-purifying catalyst 16. Thus,the combustible mixture remaining in the exhaust passage extending fromthe internal combustion engine 1 to the ignition device 17 can beremoved. As a result, no flame is generated in a broad range coveringfrom the cylinders 2 a of the internal combustion engine 1 to theignition device 17 when combustion of the mixture is started in theinternal combustion engine 1.

[0150] Moreover, according to the catalytic warming apparatus of theinternal combustion engine of the present embodiment, because ofthrottling the flow rate in the exhaust passage, the secondexhaust-purifying catalyst 16 can be heated with improved ignitabilityand combustion stability of the combustible mixture and also withimproved heat-conduction efficiency from the burned gas of thecombustible mixture to the catalyst body 16 b. As a result, rapidactivation of the catalyst body 16 b can be reliably achieved.

[0151] Embodiment 2

[0152] Hereinafter, a catalyst warming apparatus of an internalcombustion engine according to Embodiment 2 of the present inventionwill be described with reference to FIG. 6. Herein, the structuredifferent from that of Embodiment 1 will be described, but thedescription of the same structure will be omitted.

[0153] In the foregoing Embodiment 1, the fuel and air are supplied tothe exhaust pipe 14 upstream of the first exhaust-purifying catalyst 15upon cranking of the internal combustion engine 1, by injecting the fuelfrom the fuel injection valves 3 of all the cylinders 2 a, and, at thesame time, inhibiting the spark plugs 2 b of all the cylinders 2 a frombeing actuated. In the present embodiment, however, the fuel and air aresupplied to the exhaust pipe 14 upstream of the first exhaust-purifyingcatalyst 15 upon cranking of the internal combustion engine 1, byinjecting the fuel only from the fuel injection valve(s) 3 of one ormore of the cylinders 2 a, and, at the same time, inhibiting the sparkplugs 2 b of all the cylinders 2 a from being actuated.

[0154] In this case, the CPU 25 executes a catalyst-heating controlroutine as shown in FIG. 6.

[0155] The catalyst-heating control routine of FIG. 6 is a routine thatis pre-stored in the ROM 26 for execution upon starting of the internalcombustion engine 1.

[0156] In this catalyst-heating control routine, the CPU 25 firstdetermines in Step S601 whether the first or second exhaust-purifyingcatalyst 15, 16 is active or not.

[0157] When the CPU 25 determines in Step S601 that at least one of thefirst and second exhaust-purifying catalysts 15, 16 is active, the CPU25 terminates execution of this routine and executes the normal startcontrol.

[0158] On the other hand, when the CPU 25 determines in Step S601 thatboth the first and second exhaust-purifying catalysts 15, 16 areinactive, the CPU 25 proceeds to Step S602 and starts execution of thecatalyst-heating process. More specifically, the CPU 25 controls theexhaust-throttling actuator 20 so as to close the exhaust throttle valve19 to the predetermined degree. Thereafter, the CPU 25 startsapplication of the driving electric power to the starter motor, thedriving circuit(s) 5 corres-ponding to the fuel injection valve(s) 3 ofone or more of the cylinders 2 a (e.g., two cylinders), and the ignitiondevice 17, and, at the same time, inhibiting application of the drivingelectric power to the spark plugs 2 b of all the cylinders 2 a.

[0159] In this case, one or more of the cylinders 2 a having theactuated fuel injection valve(s) 3 discharge the fuel and air in theunburned state, whereas the other cylinder(s) 2 a discharge only air.The fuel and air discharged from the aforementioned one or morecylinders 2 a are supplied through the corresponding exhaust branchpipe(s) 13 to the exhaust pipe 14 upstream of the firstexhaust-purifying catalyst 15.

[0160] The fuel and air supplied to the exhaust pipe 14 upstream of thefirst exhaust-purifying catalyst 15 flow into the firstexhaust-purifying catalyst 15, where the fuel and air are sufficientlymixed together to form an excellent combustible mixture.

[0161] The combustible mixture thus formed flows out of the firstexhaust-purifying catalyst 15 into the exhaust pipe 14 downstreamthereof, and then, into the cone portion of the second exhaust-purifyingcatalyst 16. The combustible mixture flowed into the cone portion of thesecond exhaust-purifying catalyst 16 is burned by the ignition device 17provided at the cone portion, and the catalyst body 16 b of the secondexhaust-purifying catalyst 16 is heated by the flame generated by thecombustion of the combustible mixture.

[0162] Referring back to FIG. 6, the CPU 25 proceeds to Step S603subsequent to the process of Step S602, and updates a counter value ofthe first counter C1 for counting the execution time of thecatalyst-heating process.

[0163] In Step S604, the CPU 25 determines whether the counter value ofthe first counter C1 updated in Step S603 is at least equal to or higherthan the predetermined value CS1 or not, i.e., whether or not thecatalyst-heating process has been executed at least for thepredetermined time or longer.

[0164] When the CPU 25 determines in Step S604 that the counter value ofthe first counter C1 is less than the predetermined value CS1, the CPU25 repeats execution of Step S603 and subsequent steps.

[0165] When the CPU 25 determines in Step S604 that the counter value ofthe first counter C1 is equal to the predetermined value CS1 or more,the CPU 25 proceeds to Step S605 and starts execution of thecombustible-mixture removing process.

[0166] In Step S606, the CPU 25 updates a counter value of the secondcounter C2 for counting the execution time of the combustible-mixtureremoving process.

[0167] In Step S607, the CPU 25 determines whether the counter value ofthe second counter C2 updated in Step S606 is at least equal to thepredetermined value CS2 or not, i.e., whether the combustible-mixtureremoving process has been executed at least for the predetermined timeor not.

[0168] When the CPU 25 determines in Step S607 that the counter value ofthe second counter C2 is less than the predetermined value CS2, the CPU25 repeats execution of Step S606 and subsequent steps.

[0169] When the CPU 25 determines in Step S607 that the counter value ofthe second counter C2 is equal to the predetermined value CS2 or more,the CPU 25 proceeds to Step S608 and terminates execution of thecombustible-mixture removing process.

[0170] In Step S609, the CPU 25 resets the respective counter values ofthe first and second counters C1, C2 to “zero” and terminates executionof this routine. Thereafter, the CPU 25 executes the normal engine-startcontrol.

[0171] According to the above-described catalyst-heating controlroutine, the same effects as those of Embodiment 1 can be obtained.Moreover, since only the fuel injection valve(s) 3 of one or more of thecylinders 2 a are actuated, the fuel quantity required for thecatalyst-heating process can be minimized.

[0172] Note that, the foregoing description of the present embodimentexemplified a case where, when the fuel and air are supplied to theexhaust pipe 14 upstream of the first exhaust-purifying catalyst 15,actuating the fuel injection valve(s) 3 only in one or more of thecylinders 2 a, while inhibiting the spark plugs 2 b of all the cylinders2 a from being actuated. However, heating of the exhaust-purifyingcatalyst and starting of the internal combustion engine 1 may beperformed in parallel by allowing actuation of the spark plug(s) 2 b andfuel injection valve(s) 3 in the cylinder(s) 2 a other than theaforementioned one or more cylinders 2 a.

[0173] Embodiment 3

[0174] Hereinafter, a catalyst warming apparatus of an internalcombustion engine according to Embodiment 3 of the present inventionwill be described with reference to FIG. 7. Herein, the structuredifferent from that of Embodiment 1 will be described, but thedescription of the same structure will be omitted.

[0175] In Embodiment 1, the catalyst-heating control is executedimmediately before completion of starting of the internal combustionengine 1, i.e., during cranking of the internal combustion engine 1. Inthe present embodiment, however, the catalyst-heating control isperformed immediately after starting of the internal combustion engine1.

[0176] The catalyst-heating control according to the present embodimentis executed when the first and second exhaust-purifying catalysts 15, 16are inactive at the time of completion of starting the internalcombustion engine 1. In the catalyst-heating control, the CPU 25 burnsthe rich mixture in one or more of the cylinders 2 a (e.g., twocylinders) of the internal combustion engine 1 (hereinafter, suchoperation is referred to as “rich-operation”), and burns the leanmixture in the other cylinder(s) 2 a (e.g., the remaining two cylinders)(hereinafter, such operation is referred to as “lean-operation”).

[0177] In this case, the exhaust gas discharged from the above-mentionedone or more cylinders 2 a contains a large quantity of fuel in theunburned state, whereas the exhaust gas discharged from theaforementioned other cylinder(s) 2 a contains a large quantity of air(oxygen) in the unburned state.

[0178] The exhaust gas containing unburned fuel components and theexhaust gas containing unburned air are led through the exhaust branchpipes 13 into the exhaust pipe 14 upstream of the firstexhaust-purifying catalyst 15, and then, flow into the firstexhaust-purifying catalyst 15.

[0179] In the first exhaust-purifying catalyst 15, the exhaust gascontaining unburned fuel and the exhaust gas containing unburned airflow through a flow passage having an extremely smaller diameter ascompared to that of the exhaust pipe 14. Therefore, the unburned fueland air contained in the exhaust gas are sufficiently mixed as they flowthrough such flow passage.

[0180] As a result, in the exhaust gas flowing out of the firstexhaust-purifying catalyst 15, a well-mixed, excellent combustiblemixture of the fuel and air is formed. Thus, the combustible mixture isburned by the ignition device 17 in the cone portion of the secondexhaust-purifying catalyst 16.

[0181] Hereinafter, the catalyst-heating control of the presentembodiment will be described in detail.

[0182] The CPU 25 executes a catalyst-heating control routine as shownin FIG. 7 in order to execute the catalyst-heating control. Thecatalyst-heating control routine is a routine that is pre-stored in theROM 26 for execution upon starting of the internal combustion engine 1.

[0183] In the catalyst-heating control routine, the CPU 25 firstdetermines in Step S701 whether starting of the internal combustionengine 1 has been completed or not. The method of making thedetermination of completion of starting the internal combustion engine 1may include, for example, determining whether or not the engine speed isincreased at least to a predetermined value or higher.

[0184] When the CPU 25 determines in Step S701 that starting of theinternal combustion engine 1 has not been completed, the CPU 25repeatedly performs Step S701 until starting of the internal combustionengine 1 is completed.

[0185] When the CPU 25 determines in Step S701 that starting of theinternal combustion engine 1 has been completed, the CPU 25 proceeds toStep S702 and determines whether the first or second exhaust-purifyingcatalyst 15, 16 is active or not.

[0186] When the CPU 25 determines in Step S702 that at least one of thefirst and second exhaust-purifying catalysts 15, 16 is active, the CPU25 terminates execution of this routine and executes the normal startcontrol.

[0187] When the CPU 25 determines in Step S702 that both the first andsecond exhaust-purifying catalysts 15, 16 are inactive, the CPU 25proceeds to Step S703 and starts execution of catalyst-heating process.

[0188] In the catalyst-heating process, the CPU 25 performsrich-operation of, for example, first and second cylinders out of thefour cylinders 2 a of the internal combustion engine 1, by controllingthe driving circuits 5 corresponding to the first and second cylindersso as to produce the mixture having an air-fuel ratio lower than thetheoretical air-fuel ratio (i.e., rich air-fuel ratio) in the first andsecond cylinders. At the same time, the CPU 25 performs lean-operationof the remaining third and fourth cylinders, by controlling the drivingcircuits 5 corresponding to the third and fourth cylinders so as toproduce a mixture having an air-fuel ratio higher than the theoreticalair-fuel ratio (i.e., lean air-fuel ratio) in the third and fourthcylinders.

[0189] In this case, the first and second cylinders of rich-operationdischarge the exhaust gas containing a large quantity of unburned fuel,whereas the third and fourth cylinders of lean-operation discharge theexhaust gas containing a large quantity of unburned air (oxygen). Theexhaust gas discharged from the first and second cylinders (i.e., theexhaust gas containing unburned fuel) and the exhaust gas dischargedfrom the third and fourth cylinders (i.e., the exhaust gas containingunburned air) are supplied through the exhaust branch pipes 13 to theexhaust pipe 14 upstream of the first exhaust-purifying catalyst 15.

[0190] The fuel and air contained in the exhaust gas are mixed to forman excellent combustible mixture within the first exhaust-purifyingcatalyst 15. The exhaust gas containing such combustible mixture flowsout of the first exhaust-purifying catalyst 15 into the exhaust pipe 14downstream thereof, and then, from the exhaust pipe 14 into the coneportion of the second exhaust-purifying catalyst 16. The combustiblemixture flowed into the cone portion of the second exhaust-purifyingcatalyst 16 is burned by the ignition device 17 provided at the coneportion, and the catalyst body 16 b of the second exhaust-purifyingcatalyst 16 is heated by the flame generated by such combustion of thecombustible mixture.

[0191] Referring back to FIG. 7, the CPU 25 proceeds to Step S704subsequent to the process of Step S703, and updates a counter value of acounter C for counting the execution time of the catalyst-heatingprocess.

[0192] In Step S705, the CPU 25 determines whether the counter value ofthe counter C updated in Step-S704 is at least equal to a predeterminedvalue CS or not, i.e., whether or not the catalyst-heating process hasbeen executed at least for the predetermined time or longer.

[0193] When the CPU 25 determines in Step S705 that the counter value ofthe counter C is less than the predetermined value CS, the CPU 25repeats execution of Step S704 and subsequent steps.

[0194] When the CPU 25 determines in Step S705 that the counter value ofthe counter C is equal to the predetermined value CS or more, the CPU 25proceeds to Step S706, and terminates execution of the catalyst-heatingprocess. The CPU 25 resets the counter value of the counter C to “zero,”and controls the driving circuits 5 so as to render the internalcombustion engine 1 into the normal operating state.

[0195] According to the above-described catalyst-heating controlroutine, in the case where the second exhaust-purifying catalyst 16 isheated after starting of the internal combustion engine, the fuel andair can be sufficiently mixed and desirably burned without requiring aspecial pre-mixing chamber for mixing the fuel and air and a specialcombustion chamber for burning the fuel and air. because the firstexhaust-purifying catalyst 15 is disposed upstream of the secondexhaust-purifying catalyst 16, and the ignition device 17 is disposed atthe cone portion of the second exhaust-purifying catalyst 16.

[0196] As a result, when the internal combustion engine is in the normaloperating state, the heat of the exhaust gas is not transferred to thepre-mixing chamber, combustion chamber and the like, whereby the exhaustgas at a low temperature does not flow into the exhaust-purifyingcatalyst. Thus, the temperature of the exhaust-purifying catalyst can beprevented from being lowered to a value less than the activationtemperature, whereby degradation of the exhaust emissions is avoided.

[0197] Note that, in the present embodiment, the mixture having a leanair-fuel ratio is burned in the cylinder(s) 2 a which are to dischargeunburned air. However, it is also possible to inhibit fuel injection tothe cylinder(s) 2 a which are to discharge unburned air.

[0198] Embodiment 4

[0199] Hereinafter, a catalyst warming apparatus of an internalcombustion engine according to Embodiment 4 of the present inventionwill be described with reference to FIG. 8. Herein, the structuredifferent from that of Embodiment 3 will be described, but thedescription of the same structure will be omitted.

[0200] In the above-described Embodiment 3, one or more of the cylinders2 a are rich-operated so as to discharge the exhaust gas containingunburned fuel immediately after completion of starting of the internalcombustion engine 1. In the present embodiment, however, one or more ofthe cylinders 2 a are operated at a normal air-fuel ratio. Then, thefuel is secondarily injected from the corresponding fuel injectionvalve(s) 3 during the expansion or exhaust stroke of the one or morecylinders 2 a, so that the aforementioned one or more cylinders 2 a aremade to discharge the exhaust gas containing unburned fuel.

[0201] In this case, the CPU 25 executes a catalyst-heating controlroutine as shown in FIG. 8.

[0202] The catalyst-heating control routine of FIG. 8 is a routine thatis pre-stored in the ROM 26 for execution upon starting of the internalcombustion engine 1.

[0203] In the catalyst-heating control routine, the CPU 25 firstdetermines in Step S801 whether starting of the internal combustionengine 1 has been completed or not.

[0204] When the CPU 25 determines in Step S801 that starting of theinternal combustion engine 1 has not been completed, the CPU 25repeatedly performs Step S801 until starting of the internal combustionengine 1 is completed.

[0205] When the CPU 25 determines in Step S801 that starting of theinternal combustion engine 1 has been completed, the CPU 25 proceeds toStep S802 and determines whether the first or second exhaust-purifyingcatalyst 15, 16 is active or not.

[0206] When the CPU 25 determines in Step S802 that at least one of thefirst and second exhaust-purifying catalysts 15, 16 is active, the CPU25 terminates execution of this routine and executes the normal startcontrol.

[0207] When the CPU 25 determines in Step S802 that both the first andsecond exhaust-purifying catalysts 15, 16 are inactive, the CPU 25proceeds to Step S803 and starts execution of catalyst-heating process.

[0208] In the catalyst-heating process, the CPU 25, for example,controls the driving circuits 5 corresponding to first and secondcylinders out of the four cylinders 2 a of the internal combustionengine 1 so as to produce a mixture having a normal air-fuel ratio inthe first and second cylinders, and also controls these driving circuits5 so as to secondarily inject the fuel from the corresponding fuelinjection valves 3 during the exhaust stroke of the first and secondcylinders. At the same time, the CPU 25 controls the driving circuits 5corresponding to the remaining third and fourth cylinders so as toproduce a mixture having an air-fuel ratio higher than the theoreticalair-fuel ratio (i.e., lean air-fuel ratio) in the third and fourthcylinders. Thus, the CPU 25 performs lean-operation of the third andfourth cylinders.

[0209] In this case, the first and second cylinders discharge theexhaust gas containing the sub fuel, whereas the third and fourthcylinders discharge the exhaust gas containing a large quantity ofunburned air (oxygen). The exhaust gas discharged from the first andsecond cylinders (i.e., the exhaust gas containing unburned fuel) andthe exhaust gas discharged from the third and fourth cylinders (i.e.,the exhaust gas containing unburned air) are supplied through theexhaust branch pipes 13 to the exhaust pipe 14 upstream of the firstexhaust-purifying catalyst 15.

[0210] The fuel and air contained in the exhaust gas are mixed to forman excellent combustible mixture within the first exhaust-purifyingcatalyst 15. The exhaust gas containing such combustible mixture flowsout of the first exhaust-purifying catalyst 15 into the exhaust pipe 14downstream thereof, and then, flows into the cone portion of the secondexhaust-purifying catalyst 16. The combustible mixture flowing into thecone portion of the second exhaust-purifying catalyst 16 is burned bythe ignition device 17 provided at the cone portion, and the catalystbody 16 b of the second exhaust-purifying catalyst 16 is heated by theflame generated by such combustion.

[0211] Referring back to FIG. 8, the CPU 25 proceeds to Step S804subsequent to the process of Step S803, and updates a counter value ofthe counter C for counting the execution time of the catalyst-heatingprocess.

[0212] In Step S805, the CPU 25 determines whether the counter value ofthe counter C updated in the Step S804 is at least equal to thepredetermined value CS or not, i.e., whether or not the catalyst-heatingprocess has been executed at least for the predetermined time or longer.

[0213] When the CPU 25 determines in Step S805 that the counter value ofthe counter C is less than the predetermined value CS, the CPU 25repeats execution of Step S804 and subsequent steps.

[0214] When the CPU 25 determines in Step S805 that the counter value ofthe counter C is equal to the predetermined value CS or more, the CPU 25proceeds to Step S806, and terminates execution of the catalyst-heatingprocess. The CPU 25 resets the counter value of the counter C to “zero,”and controls the driving circuits 5 so as to render the internalcombustion engine 1 into the normal operating state.

[0215] According to the above-described catalyst-heating controlroutine, the same effects as those of Embodiment 3 can be obtained.

[0216] Embodiment 5

[0217] Hereinafter, a catalyst warming apparatus of an internalcombustion engine according to Embodiment 5 of the present inventionwill be described with reference to FIGS. 9 to 11. Herein, the structuredifferent from that of Embodiment 3 will be described, but thedescription of the same structure will be omitted.

[0218] In the above-described Embodiment 3, in the case where theunburned fuel and air are supplied upstream of the firstexhaust-purifying catalyst 15 immediately after completion of startingof the internal combustion engine 1, one or more of the cylinders 2 a ofthe internal combustion engine 1 are rich-operated, whereas the othercylinder(s) 2 a are lean-operated. As a result, the aforementioned oneor more cylinders 2 a discharge the exhaust gas containing unburnedfuel, whereas the aforementioned other cylinder(s) 2 a discharge theexhaust gas containing unburned air. In the present embodiment, however,all the cylinders 2 a of the internal combustion engine 1 arerich-operated, and the sub air is supplied to the exhaust gas dischargedfrom all the cylinders 2 a. Thus, the exhaust gas containing unburnedfuel and unburned air is supplied upstream of the firstexhaust-purifying catalyst 15.

[0219] Each exhaust branch pipe 13 connected to the internal combustionengine 1 is provided with a sub air injection nozzle 32 having itsinjection port facing the exhaust port of the corresponding cylinder 2a, as shown in FIG. 9.

[0220] As shown in FIG. 10, the sub air injection nozzles 32 areconnected to the output port 31 of the ECU 23 through electrical wiring,and the sub air injection nozzles 32 are opened in response toapplication of the electric driving power from the ECU 23, and injectthe sub air supplied from an unillustrated air pump into the exhaustports of the respective cylinders 2 a.

[0221] Hereinafter, the catalyst-heating control of the presentembodiment will be described.

[0222] According to the present embodiment, the CPU 25 executes acatalyst-heating control routine as shown in FIG. 11 in order to executethe catalyst-heating control. This catalyst-heating control routine is aroutine that is pre-stored in the ROM 26 for execution at the time ofstarting of the internal combustion engine 1.

[0223] In the catalyst-heating control routine, the CPU 25 firstdetermines in Step S1101 whether starting of the internal combustionengine 1 has been completed or not.

[0224] When the CPU 25 determines in Step S1101 that starting of theinternal combustion engine 1 has not been completed, the CPU 25repeatedly performs Step S1101 until starting of the internal combustionengine 1 is completed.

[0225] When the CPU 25 determines in Step S1101 that starting of theinternal combustion engine 1 has been completed, the CPU 25 proceeds toStep S1102 and determines whether the first or second exhaust-purifyingcatalyst 15, 16 is active or not.

[0226] When the CPU 25 determines in Step S1102 that at least one of thefirst and second exhaust-purifying catalysts 15, 16 is active, the CPU25 terminates execution of this routine and executes the normal startcontrol.

[0227] When the CPU 25 determines in Step S1102 that both the first andsecond exhaust-purifying catalysts 15, 16 are inactive, the CPU 25proceeds to Step S1103 and starts the catalyst-heating process.

[0228] In the catalyst-heating process, the CPU 25 performs, forexample, the rich-operation of all the cylinders 2 a of the internalcombustion engine 1 so as to discharge the exhaust gas containing alarge quantity of unburned fuel from all the cylinders 2 a. At the sametime, the CPU 25 applies the driving electric power to the sub airinjection nozzles 32 so as to inject the sub air to the exhaust ports ofthe respective cylinders 2 a.

[0229] In this case, the exhaust gas containing a large quantity ofunburned fuel and the sub air are supplied to the exhaust ports of allthe cylinders 2 a of the internal combustion engine 1. The exhaust gasand the sub air are led from the exhaust ports to the exhaust branchpipes 13, and then, flow through the exhaust pipe 14 into the firstexhaust-purifying catalyst 15.

[0230] The unburned fuel contained in the exhaust gas and the sub airare mixed to form an excellent combustible mixture within the firstexhaust-purifying catalyst 15. The exhaust gas containing suchcombustible mixture flows out of the first exhaust-purifying catalyst 15into the exhaust pipe 14 downstream thereof, and then, flows into thecone portion of the second exhaust-purifying catalyst 16. Thecombustible mixture flowing into the cone portion of the secondexhaust-purifying catalyst 16 is burned by the ignition device 17provided at the cone portion, and the catalyst body 16 b of the secondexhaust-purifying catalyst 16 is heated by the flame generated by suchcombustion.

[0231] Referring back to FIG. 11, the CPU 25 proceeds to Step S1104subsequent to the process of Step S1103, and updates a counter value ofthe counter C for counting the execution time of the catalyst-heatingprocess.

[0232] In Step S1105, the CPU 25 determines whether the counter value ofthe counter C updated in the Step S1104 is at least equal to thepredetermined value CS or not, i.e., whether or not the catalyst-heatingprocess has been executed at least for the predetermined time or longer.

[0233] When the CPU 25 determines in Step S1105 that the counter valueof the counter C is less than the predetermined value CS, the CPU 25repeats execution of Step S1104 and subsequent steps.

[0234] When the CPU 25 determines in Step S1105 that the counter valueof the counter C is equal to the predetermined value CS or more, the CPU25 proceeds to Step S1106, and terminates execution of thecatalyst-heating process. The CPU 25 resets the counter value of thecounter C to “zero,” and controls the driving circuits 5 so as to renderthe internal combustion engine 1 into the normal operating state.

[0235] According to the above-described catalyst-heating controlroutine, the same effects as those of Embodiment 3 can be obtained.

[0236] Embodiment 6

[0237] Hereinafter, a catalyst warming apparatus of an internalcombustion engine according to Embodiment 6 of the present inventionwill be described with reference to FIG. 12. Herein, the structuredifferent from that of Embodiment 5 will be described, but thedescription of the same structure will be omitted.

[0238] In the above-described Embodiment 5, in the case when the exhaustgas containing unburned fuel and air is supplied upstream of the firstexhaust-purifying catalyst 15 immediately after completion of startingof the internal combustion engine 1, all the cylinders 2 a of theinternal combustion engine 1 are rich-operated, and the sub air issupplied to the exhaust gas discharged from all the cylinders 2 a. Inthe present embodiment, however, all the cylinders 2 a of the internalcombustion engine 1 are operated at a normal air-fuel ratio. During theexhaust stroke of the cylinders 2 a, the fuel is secondarily injectedfrom the respective fuel injection valves 3, and the sub air is injectedfrom the respective sub air injection nozzles 32. Thus, the exhaust gascontaining unburned fuel (sub fuel) and unburned air (sub air) issupplied upstream of the first exhaust-purifying catalyst 15.

[0239] In this case, the CPU 25 executes a catalyst-heating controlroutine as shown in FIG. 12.

[0240] The catalyst-heating control routine of FIG. 12 is a routine thatis pre-stored in the ROM 26 for execution at the time of starting of theinternal combustion engine 1.

[0241] In the catalyst-heating control routine, the CPU 25 firstdetermines in Step S1201 whether starting of the internal combustionengine 1 has been completed or not.

[0242] When the CPU 25 determines in Step S1201 that starting of theinternal combustion engine 1 has not been completed, the CPU 25repeatedly performs Step S1201 until starting of the internal combustionengine 1 is completed.

[0243] When the CPU 25 determines in Step S1201 that starting of theinternal combustion engine 1 has been completed, the CPU 25 proceeds toStep S1202 and determines whether the first or second exhaust-purifyingcatalyst 15, 16 is active or not.

[0244] When the CPU 25 determines in Step S1202 that at least one of thefirst and second exhaust-purifying catalysts 15, 16 is active, the CPU25 terminates execution of this routine and executes the normal startcontrol.

[0245] When the CPU 25 determines in Step S1202 that both the first andsecond exhaust-purifying catalysts 15, 16 are inactive, the CPU 25proceeds to Step S1203 and starts the catalyst-heating process.

[0246] In the catalyst-heating process, the CPU 25, for example,operates all the cylinders 2 a of the internal combustion engine 1 at anormal air-fuel ratio. During the exhaust stroke of the cylinders 2 a,the CPU 25 secondarily injects the fuel from the respective fuelinjection valves 3 so that the exhaust gas containing unburned sub fuelis discharged from the cylinders 2 a. Moreover, the CPU 25 applies thedriving electric power to the sub air injection nozzles 32 so as toinject the sub air to the exhaust ports of the respective cylinders 2 a.

[0247] In this case, the exhaust gas containing a large quantity ofunburned sub fuel and the sub air are supplied to the exhaust ports ofall the cylinders 2 a of the internal combustion engine 1. The exhaustgas and the sub air are led from the exhaust ports to the exhaust branchpipes 13, and then, flow through the exhaust pipe 14 into the firstexhaust-purifying catalyst 15.

[0248] The unburned sub fuel contained in the exhaust gas and the subair are mixed to form an excellent combustible mixture within the firstexhaust-purifying catalyst 15. The exhaust gas containing suchcombustible mixture flows out of the first exhaust-purifying catalyst 15into the exhaust pipe 14 downstream thereof, and then, flows into thecone portion of the second exhaust-purifying catalyst 16. Thecombustible mixture flowing into the cone portion of the secondexhaust-purifying catalyst 16 is burned by the ignition device 17provided at the cone portion, and the catalyst body 16 b of the secondexhaust-purifying catalyst 16 is heated by the flame generated by suchcombustion.

[0249] Referring back to FIG. 12, the CPU 25 proceeds to Step S1204subsequent to the process of Step S1203, and updates a counter value ofthe counter C for counting the execution time of the catalyst-heatingprocess.

[0250] In Step S1205, the CPU 25 determines whether the updated countervalue of the counter C is at least equal to the predetermined value CSor not, i.e., whether or not the catalyst-heating process has beenexecuted at least for the predetermined time or longer.

[0251] When the CPU 25 determines in Step S1205 that the counter valueof the counter C is less than the predetermined value CS, the CPU 25repeats execution of Step S1204 and subsequent steps.

[0252] When the CPU 25 determines in Step S1205 that the counter valueof the counter C is equal to the predetermined value CS or more, the CPU25 proceeds to Step S1206, and terminates execution of thecatalyst-heating process. The CPU 25 resets the counter value of thecounter C to “zero,” and controls the driving circuits 5 so as to renderthe internal combustion engine 1 into the normal operating state.

[0253] According to the above-described catalyst-heating controlroutine, the same effects as those of Embodiment 5 can be obtained,while operating the internal combustion engine 1 at a normal air-fuelratio.

[0254] Embodiment 7

[0255] Hereinafter, a catalyst warming apparatus of an internalcombustion engine according to Embodiment 7 of the present inventionwill be described with reference to FIGS. 13 to 15. Herein, thestructure different from that of Embodiment 3 will be described, but thedescription of the same structure will be omitted.

[0256] In the above-described Embodiment 3, in the case whereimmediately after completion of starting of the internal combustionengine 1, one or more of the cylinders 2 a are rich-operated so as todischarge the exhaust gas containing unburned fuel from the one or moreof the cylinders 2 a. In the present embodiment, however, a so-calledexhaust gas recirculation (EGR) is carried out for recirculating theexhaust gas to one or more of the cylinders 2 a so that low-temperaturecombustion is performed in the one or more cylinders 2 a. Thus, thecombustion temperature of the mixture in the aforementioned one or morecylinders 2 a is lowered, whereby the exhaust gas containing a largequantity of unburned fuel components is discharged.

[0257] As shown in FIG. 13, an exhaust-gas-recirculation (EGR) passage33 is connected to the exhaust branch pipes 13. The EGR passage 33branches to be connected to each intake branch pipe 6. Anexhaust-gas-recirculation (EGR) valve 34 for enabling and blockingcommunication between the EGR passage 33 and the corresponding intakebranch pipe 6 is provided at the connection between the EGR passage 33and each intake branch pipe 6.

[0258] As shown in FIG. 14, the EGR valves 34 are connected to theoutput port 31 of the ECU 23 through electrical wiring, so that the EGRvalves 14 are opened and closed according to a control current from theECU 23.

[0259] Hereinafter, the catalyst-heating control according to thepresent embodiment will be described.

[0260] In the present embodiment, the CPU 25 executes a catalyst-heatingcontrol routine as shown in FIG. 15 in order to execute thecatalyst-heating control. The catalyst-heating control routine is aroutine that is pre-stored in the ROM 26 for execution at the time ofstarting of the internal combustion engine 1.

[0261] In the catalyst-heating control routine, the CPU 25 firstdetermines in Step S1501 whether starting of the internal combustionengine 1 has been completed or not.

[0262] When the CPU 25 determines in Step S1501 that starting of theinternal combustion engine 1 has not been completed, the CPU 25repeatedly performs Step S1501 until starting of the internal combustionengine 1 is completed.

[0263] When the CPU 25 determines in Step S1501 that starting of theinternal combustion engine 1 has been completed, the CPU 25 proceeds toStep S1502 and determines whether the first or second exhaust-purifyingcatalyst 15, 16 is active or not.

[0264] When the CPU 25 determines in Step S1502 that at least one of thefirst and second exhaust-purifying catalysts 15, 16 is active, the CPU25 terminates execution of this routine and executes the normal startcontrol.

[0265] When the CPU 25 determines in Step S1502 that both the first andsecond exhaust-purifying catalysts 15, 16 are inactive, the CPU 25proceeds to Step S1503 and starts the catalyst-heating process.

[0266] In the catalyst-heating process, the CPU 25, for example, opensthe EGR valve(s) 34 corresponding to one or more of the cylinders 2 a(e.g., first and second cylinders) of the internal combustion engine 1for low-temperature combustion. Thus, the exhaust gas containing arelatively large quantity of unburned fuel components is discharged fromthe aforementioned one or more cylinders 2 a. At the same time, the CPU25 performs lean-operation of the other cylinder(s) 2 a (e.g., third andfourth cylinders), whereby the exhaust gas containing a relatively largequantity of unburned air is discharged from the other cylinder(s) 2 a.

[0267] In this case, the first and second cylinders discharge theexhaust gas containing a large quantity of unburned fuel, whereas thethird and fourth cylinders discharge the exhaust gas containing a largequantity of unburned air (oxygen). The exhaust gas discharged from thefirst and second cylinders (i.e., the exhaust gas containing unburnedfuel) and the exhaust gas discharged from the third and fourth cylinders(i.e., the exhaust gas containing unburned air) are supplied through theexhaust branch pipes 13 to the exhaust pipe 14 upstream of the firstexhaust-purifying catalyst 15.

[0268] The fuel and air contained in the exhaust gas are mixed to forman excellent combustible mixture within the first exhaust-purifyingcatalyst 15. The exhaust gas containing such combustible mixture flowsout of the first exhaust-purifying catalyst 15 into the exhaust pipe 14downstream thereof, and then, flow into the cone portion of the secondexhaust-purifying catalyst 16. The combustible mixture flowing into thecone portion of the second exhaust-purifying catalyst 16 is burned bythe ignition device 17 provided at the cone portion, and the catalystbody 16 b of the second exhaust-purifying catalyst 16 is heated by theflame generated by such combustion.

[0269] Referring back to FIG. 15, the CPU 25 proceeds to Step S1504subsequent to the process of Step S1503, and updates a counter value ofthe counter C for counting the execution time of the catalyst-heatingprocess.

[0270] In Step S1505, the CPU 25 determines whether the updated countervalue of the counter C is at least equal to the predetermined value CSor not, i.e., whether or not the catalyst-heating process has beenexecuted at least for the predetermined time or longer.

[0271] When the CPU 25 determines in Step S1505 that the counter valueof the counter C is less than the predetermined value CS, the CPU 25repeats execution of Step S1504 and subsequent steps.

[0272] When the CPU 25 determines in Step S1505 that the counter valueof the counter C is equal to the predetermined value CS or more, the CPU25 proceeds to Step S1506, and terminates execution of thecatalyst-heating process. The CPU 25 resets the counter value of thecounter C to “zero,” and controls the driving circuits 5 so as to renderthe internal combustion engine 1 into the normal operating state.

[0273] According to the above-described catalyst-heating controlroutine, the same effects as those of Embodiment 3 can be obtained.

What is claimed is:
 1. A catalyst warming apparatus of an internalcombustion engine, comprising: an exhaust passage connected to theinternal combustion engine; a main exhaust-purifying catalyst providedin said exhaust passage for purifying exhaust gas flowing in saidexhaust passage; a sub exhaust-purifying catalyst provided in saidexhaust passage upstream of said main exhaust-purifying catalyst forpurifying the exhaust gas flowing in said exhaust passage; ignitionmeans provided in said exhaust passage between said main and subexhaust-purifying catalysts; and combustible-component supply means forsupplying fuel and air to the exhaust passage upstream of said subexhaust-purifying catalyst; wherein said combustible-component supplymeans supplies the fuel and air to the exhaust passage upstream of saidsub exhaust-purifying catalyst immediately after completion of startingof said internal combustion engine.
 2. A catalyst warming apparatus ofan internal combustion engine according to claim 1, wherein saidcombustible-component supply means supplies the fuel and air to theexhaust passage upstream of said sub exhaust-purifying catalyst, bycausing at least one of the cylinders of said internal combustion engineto discharge exhaust gas containing unburned fuel, and, at the sametime, causing the remainder of the cylinders to discharge exhaust gascontaining unburned air immediately after completion of starting of saidinternal combustion engine.
 3. A catalyst warming apparatus of aninternal combustion engine according to claim 2, wherein saidcombustible-component supply means causes said at least one of thecylinders to discharge the exhaust gas containing unburned fuel, byburning a rich mixture in said at least one of the cylinders.
 4. Acatalyst warming apparatus of an internal combustion engine according toclaim 2, wherein said combustible-component supply means causes said atleast one of the cylinders to discharge the exhaust gas containingunburned fuel, by injecting main fuel for combustion from a fuelinjection valve of said at least one of the cylinders, and then,injecting sub fuel therefrom.
 5. A catalyst warming apparatus of aninternal combustion engine according to claim 2, wherein saidcombustible-component supply means causes said at least one of thecylinders to discharge the exhaust gas containing unburned fuel, bycausing low-temperature combustion to occur in said at least one of thecylinders.
 6. A catalyst warming apparatus of an internal combustionengine according to claim 2, wherein said combustible-component supplymeans causes said remainder of the cylinders to discharge the exhaustgas containing unburned air, by burning a lean mixture in said remainderof the cylinders.
 7. A catalyst warming apparatus of an internalcombustion engine according to claim 2, wherein saidcombustible-component supply means causes said remainder of thecylinders to discharge the exhaust gas containing unburned air, byinhibiting actuation of a fuel injection valve of each of said remainderof the cylinders.
 8. A catalyst warming apparatus of an internalcombustion engine according to claim 1, wherein saidcombustible-component supply means supplies the fuel and air to theexhaust passage upstream of said sub exhaust-purifying catalyst, byburning a rich mixture in every cylinder of said internal combustionengine as well as supplying sub air to the exhaust passage upstream ofsaid sub exhaust-purifying catalyst immediately after completion ofstarting of said internal combustion engine.